The recommended route of administration and dosages for each vaccine are specified on package inserts. Most vaccines for adults are given by subcutaneous (SC) or intramuscular (IM) injection. When administering vaccines, it is imperative to aspirate before depressing the plunger to make certain that the product will not be injected intravenously. This can result in increased adverse effects and may also reduce the immune response.
It is also important that a needle 1-1.5 inches long be used for IM delivery of vaccines containing aluminium phosphate (e.g., HBV, Td, and Tdap vaccines). Subcutaneous administration of such vaccines can lead to local tissue necrosis. Intramuscular injections should be given in the deltoid muscle. Studies with the hepatitis B vaccine have shown that its immunogenicity is significantly reduced when given in the buttocks. This observation may apply to other vaccines as well.